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Reflectance, Transmittance, and Absorptance of Light by Subcellular Particles of Spinach (Spinacia oleracea L.) Leaves¹

This study considered the premise that subcellular particles in leaves contribute to the reflectance (R) and absorptance (A) of near-infrared (IR) (light 750 to 350 nm).

Subcellular particles of spinach (Spinacia oleracea L.) leaves were differentially sedimented and resuspended in a buffered sucrose solution. A spectroreflectometer was used to measure R and transmittance (T) over the 500- to 2,500-rim wavelength interval (WLI) on replicated aliquots of five preparations: buffered sucrose solution (control); chloroplast preparation; S1, sediment of chloroplast preparation supernatant; $2, sediment of S1 supernatant; and S3, sediment of S2 supernatant. Absorptance was calculated: A= 1 - (R + T).

All suspensions of particulates caused less R than the buffered sucrose solution over the 500- to 650-nm WLI. The chloroplast preparation, compared with the buffered sucrose solution, increased R over the 750- to 950-nm WLI.

The chloroplast preparation, compared with the buffered sucrose solution, S2, and S3, decreased T over the 500- to 1,250-nm WLI; SI decreased T over the 500- to 900- nm WLI.

Compared with remaining treatments, the chloroplast preparation increased A over the 500- to 1,100-nm WLI.

Excluding the buffered sucrose solution, R and A increased and T decreased in the IR region as particle size increased.

A conclusion was reached that subcellular particles in leaves contribute to the R and A of IR light.

Key Words: Chloroplasts • Near-infrared light • Refractive index

² Plant Physiologist, USDA, Weslaco, Texas 78596.

Received for publication April 6, 1972.